Figures

Exosuits (A) use garment-like functional textile anchors worn around the waist and calf (B) and Bowden cable-based mechanical power transmissions to generate assistive joint torques as a function of the paretic gait cycle (C). Integrated sensors (load cells and gyroscopes) are used to detect gait events and in a cable position–based force controller that modulates force delivery. The contractile elements of the exosuit are the Bowden cables located posterior and anterior to the ankle joint. Exosuit-generated PF and DF forces are designed to restore the paretic limb’s contribution to forward propulsion (GRF) and ground clearance (ankle DF angle during swing phase)—subtasks of walking that are impaired after stroke. Poststroke deficits in these variables are demonstrated through a comparison of paretic (black) and nonparetic (gray) limbs. Means across participants are presented (n = 7).

Fig. 2.Illustration of experimental setup.

Ground reaction force and kinematic data were collected concurrently with metabolic data as participants walked on an instrumented treadmill with the exosuit worn either powered (delivering forces generated by an off-board actuation unit) or unpowered. Participants were harnessed, but no body weight was supported. Participants were allowed to hold a side-mounted handrail if necessary for safety.

(A) Commanded position trajectories (blue) translate to exosuit-generated forces (red) based on the exosuit-human series stiffness. This parameter reflects the interaction of the cable position command with the compliance inherent to the textiles, cables, and human tissue. On a step-by-step basis, the timing of exosuit-generated force delivery is controlled as a function of gait subphases identified using shoe-mounted gyroscope sensors (GY). The amplitude of force produced by the exosuit is measured by load cells (LC) that measure the force delivered at the ankle—one for each PF and DF (only PF is shown). The delivered force is continuously monitored, and adjustments are made by the controller to maintain specific features of the delivered force profile. (B) Average exosuit-generated PF forces as a function of the paretic gait cycle (x axis). Two ankle PF force delivery onset timings were evaluated. PF forces were delivered during terminal stance or about 10% earlier in the paretic gait cycle, during midstance. (C) Variability in commanded force parameters (x axis). The force features prescribed by the controller on a step-by-step basis included the onset timing of PF force (PF onset), the peak amplitude of PF force (PF peak)—constrained to 25% bw, the onset timing of DF force (DF onset), and the off time of DF force (DF offset). (D) Relative changes (%Δ) in participants’ interlimb propulsion symmetry based on the onset timing of exosuit-generated PF forces. Four participants benefited more from a late onset of PF force timing, two participants benefited more from an early onset, and one participant (#1) benefited equally from both timings. Means and SE are presented in (C) and (D). *P < 0.05.

*The participant’s actual 10-m overground walk test speed was higher than the speed tested on the treadmill. Participant #01’s actual overground speed was 1.16 m/s, but this participant was not safe walking at this speed on the treadmill. Participant #07’s speed was 1.72 m/s, but this speed was beyond the capabilities of the electromechanical actuator used for this study.